Data Center Cooling System

ABSTRACT

A data center has a room having a cold aisle and a hot aisle and a plurality of electronic components disposed between the cold and hot aisles. At least one air-to-liquid heat exchanger is disposed between the hot and cold aisles. At least one first fan circulates air in the room at a first flow rate. The at least one first fan circulates air through the at least one air-to-liquid heat exchanger from the hot aisle to the cold aisle. An air supply system is fluidly connected to the room. The air supply system includes an air filter, and a second fan supplying air from outside the room to the room at a second flow rate. The second flow rate is lower than the first flow rate. A data center cooling system and a data center having the data center cooling system are also disclosed.

FIELD OF THE INVENTION

The present invention relates to data center cooling systems, methods ofcooling data centers, and data centers having such systems and usingsuch methods.

BACKGROUND

A data center is a facility inside which are stored at least one ofgeneral or special purpose computers, servers, electronic data storage,telecommunication devices, and combinations thereof. These electroniccomponents are typically stored in racks inside the data center. Aswould be understood, in order to operate, the electronic components needto be supplied with electricity. During operation of the electroniccomponents, a major portion of the electricity used by the components isconverted to heat.

In order for these components to operate efficiently, they have tooperate in a controlled environment where there is very little dust andwhere the humidity and temperature are also controlled. As such, theheat generated by the electronic components has to be removed in orderfor the electronic components to operate within an acceptable range oftemperature and to avoid failures of these components. The amount ofpower and the costs used for the removal of this heat is one of themajor sources of power consumption and costs associated with theoperation of data centers.

The efficiency of a data center is typically defined by a parameterreferred to as the Power Usage Effectiveness (PUE). The PUE is the ratioof the total power consumed by the data center to the power consumed bythe electronic components. As such, by reducing the amount of powernecessary to cool the data center, the PUE of the data center alsoimproves, which typically translates into lower operating costs.

Therefore, there is a need for a system for cooling a data center. Thereis also a need for a method of cooling a data center. There is also aneed for a data center using such a system and/or method.

SUMMARY

It is an object of the present invention to ameliorate at least some ofthe inconveniences present in the prior art.

In one aspect, the present provides a data center having a room having acold aisle and a hot aisle and a plurality of electronic componentsdisposed between the cold aisle and the hot aisle. Air in the roomcirculating through the plurality of electronic components from the coldaisle to the hot aisle. At least one air-to-liquid heat exchanger isdisposed between the hot aisle and the cold aisle. At least one firstfan circulates air in the room at a first flow rate. The at least onefirst fan circulates air through the at least one air-to-liquid heatexchanger from the hot aisle to the cold aisle. An air supply system isfluidly connected to the room for supplying air from outside the room tothe room. The air supply system includes an air filter, and a second fansupplying air from outside the room to the room at a second flow rate.The second flow rate is lower than the first flow rate.

In an additional aspect, the at least one air-to-liquid heat exchangeris filterless.

In a further aspect, the second flow rate is between 0.1% and 25% of thefirst flow rate.

In an additional aspect, the second flow rate is between 2% and 5% ofthe first flow rate.

In a further aspect, the at least one air-to-liquid heat exchanger is atleast one first air-to-liquid heat exchanger. The air supply systemfurther includes at least one second air-to-liquid heat exchanger. Theat least one second fan circulates air through the at least one secondair-to-liquid heat exchanger.

In an additional aspect, the at least one second air-to-liquid heatexchanger selectively heats the air from the outside before the air issupplied to the room using hot coolant exiting the at least one firstair-to-liquid heat exchanger. The at least one second air-to-liquid heatexchanger selectively cools the air from the outside before the air issupplied to the room using cool coolant supplied to the at least onefirst air-to-liquid heat exchanger.

In a further aspect, a liquid-to-liquid heat exchanger is fluidlyconnected to the at least one second air-to-liquid heat exchanger. Atleast one pump circulates coolant between the liquid-to-liquid heatexchanger and the at least one second air-to-liquid heat exchanger. Atleast one valve selectively supplies one of the hot coolant and the coolcoolant to the liquid-to-liquid heat exchanger.

In an additional aspect, at least one valve selectively supplies one ofthe hot coolant and the cool coolant to the second air-to-liquid heatexchanger. At least one pump circulates the one of the hot coolant andthe cool coolant through the second air-to-liquid heat exchanger.

In a further aspect, the air supply system further includes anair-to-coolant heat exchanger disposed downstream of at least one secondair-to-liquid heat exchanger, and an autonomous refrigeration systemfluidly connected to the air-to-coolant heat exchanger. The autonomousrefrigeration system cools coolant flowing through the air-to-coolantheat exchanger.

In an additional aspect, the air-to-coolant heat exchanger is a thirdair-to-liquid heat exchanger.

In a further aspect, the hot coolant is at a temperature of at least 18degrees Celsius and the cool coolant is at a temperature between 8degrees Celsius and 18 degrees Celsius.

In an additional aspect, the coolant is at least one of water andantifreeze.

In a further aspect, at least one air temperature sensor is disposed inthe hot aisle for sensing an air temperature in the hot aisle, at leastone first air pressure sensor is disposed in the hot aisle for sensingan air pressure in the hot aisle, and at least one second air pressuresensor is disposed in the cold aisle for sensing an air pressure in thecold aisle. A speed of the at least one first fan is increased toincrease the first flow rate such that the air pressure in the coldaisle is increased relative to the hot aisle when the air temperature inthe hot aisle is above a predetermined temperature. The speed of the atleast one first fan is decreased to decrease the first flow rate suchthat the air pressure in the cold aisle is decreased relative to the hotaisle when the air temperature in the hot aisle is below thepredetermined temperature.

In an additional aspect, the second flow rate is substantially constant.

In a further aspect, the predetermined temperature is between 26 degreesCelsius and 38 degrees Celsius.

In an additional aspect, at least one air temperature sensor is disposedin the cold aisle for sensing an air temperature in the cold aisle. Aflow rate of coolant in the at least one air-to-liquid heat exchanger isincreased when the air temperature in the cold aisle is above apredetermined temperature. The flow rate of coolant in the at least oneair-to-liquid heat exchanger is decreased when the air temperature inthe cold aisle is below the predetermined temperature.

In a further aspect, a temperature of coolant supplied to the at leastone air-to-liquid heat exchanger is substantially constant.

In an additional aspect, the predetermined temperature is between 15degrees Celsius and 25 degrees Celsius.

In a further aspect, the at least one air temperature sensor is disposedin the cold aisle for sensing an air temperature in the cold aisle. Atemperature of coolant supplied to the at least one air-to-liquid heatexchanger is decreased when the air temperature in the cold aisle isabove a predetermined temperature. The temperature of coolant suppliedto the at least one air-to-liquid heat exchanger is increased when theair temperature in the cold aisle is below the predeterminedtemperature.

In an additional aspect, a plurality of racks is disposed between thecold aisle and the hot aisle. The plurality of electronic components isdisposed in the plurality of racks.

In another aspect, the present provides a data center cooling systemhaving at least one air-to-liquid heat exchanger adapted to cool airfrom a hot aisle of at least one room of a data center, aliquid-to-liquid heat exchanger fluidly connected to the at least oneair-to-liquid heat exchanger, a first chiller fluidly connected to theliquid-to-liquid heat exchanger, a second chiller fluidly connected tothe first chiller, at least one first pump fluidly connected to the atleast one air-to-liquid heat exchanger for pumping a first coolant fromthe at least one air-to-liquid heat exchanger, the first coolant flowingselectively to the liquid-to-liquid heat exchanger, and to the first andsecond chillers prior to flowing back to the at least one air-to-liquidheat exchanger, a free cooling unit fluidly connected to theliquid-to-liquid heat exchanger for cooling the first coolant flowingtherethrough and fluidly connected to the first and second chillers forcondensing refrigerant circulated therein, and at least one second pumpfluidly connected to the free cooling unit for pumping a second coolantfrom the free cooling unit, the second coolant flowing selectively tothe liquid-to-liquid heat exchanger, and to the first and secondchillers prior to flowing back to the free cooling unit. The at leastone air-to-liquid heat exchanger, the liquid-to-liquid heat exchanger,the first chiller and the second chiller are fluidly connected inseries. When the first coolant flows to the liquid-to-liquid heatexchanger and to the first and second chillers, the first coolant flowssequentially from the at least one air-to-liquid heat exchanger, to theliquid-to-liquid heat exchanger, to the first chiller, to the secondchiller, and back to the at least one air-to-liquid heat exchanger.

In a further aspect, the free cooling unit, the liquid-to-liquid heatexchanger, the first chiller and the second chiller are connected inseries.

In an additional aspect, when the second coolant flows to theliquid-to-liquid heat exchanger and to the first and second chillers,the second coolant flows sequentially from the free cooling unit, to theliquid-to-liquid heat exchanger, to the second chiller, to the firstchiller, and back to the free cooling unit.

In a further aspect, the free cooling unit is a cooling tower and thesecond coolant is water.

In an additional aspect, the free cooling unit is a dry cooler.

In a further aspect, the second coolant is at least in part antifreeze.

In an additional aspect, a first valve has a first position where thesecond coolant flows through the liquid-to-liquid heat exchanger and asecond position where at least a portion of the second coolant bypassesthe liquid-to-liquid heat exchanger, a second valve has a first positionwhere the second coolant flows through the first chiller and a secondposition where at least a portion of the second coolant bypasses thefirst chiller, and a third valve has a first position where the secondcoolant flows through the second chiller and a second position where atleast a portion of the second coolant bypasses the second chiller.

In a further aspect, the at least one second pump is fluidly connectedbetween the free cooling unit and the liquid-to-liquid heat exchanger.

In an additional aspect, a first valve has a first position where thefirst coolant flows through the liquid-to-liquid heat exchanger and asecond position where at least a portion of the first coolant bypassesthe liquid-to-liquid heat exchanger, a second valve has a first positionwhere the first coolant flows through the first chiller and a secondposition where at least a portion of the first coolant bypasses thefirst chiller, and a third valve has a first position where the firstcoolant flows through the second chiller and a second position where atleast a portion of the first coolant bypasses the second chiller.

In a further aspect, a fourth valve has a first position where thesecond coolant flows through the liquid-to-liquid heat exchanger and asecond position where at least a portion of the second coolant bypassesthe liquid-to-liquid heat exchanger, a fifth valve has a first positionwhere the second coolant flows through the first chiller and a secondposition where at least a portion of the second coolant bypasses thefirst chiller, a sixth valve has a first position where the secondcoolant flows through the second chiller and a second position where atleast a portion of the second coolant bypasses the second chiller. Thefourth valve is in the first position when the first valve is in thefirst position. The fifth valve is in the first position when the secondvalve is in the first position. The sixth valve is in the first positionwhen the third valve is in the first position. The fourth valve is inthe second position when the first valve is in the second position. Thefifth valve is in the second position when the second valve is in thesecond position. The sixth valve is in the second position when thethird valve is in the second position.

In an additional aspect, a first temperature sensor senses a temperatureof the first coolant upstream of the liquid-to-liquid heat exchanger,and a second temperature sensor senses a temperature of the secondcoolant upstream of the liquid-to-liquid heat exchanger. The first valveis in the second position at least when the temperature of the secondcoolant sensed by the second temperature sensor is above the temperatureof the first coolant sensed by the first temperature sensor.

In a further aspect, the first valve is in the first position when thetemperature of the second coolant sensed by the second temperaturesensor is below the temperature of the first coolant sensed by the firsttemperature sensor by at least a predetermined amount.

In an additional aspect, the predetermined amount is between 0.1 and 10degrees.

In a further aspect, a temperature sensor senses a temperature of thefirst coolant downstream of the liquid-to-liquid heat exchanger andupstream of the first chiller. The second valve is in the secondposition when the temperature of the first coolant sensed by thetemperature sensor is at or below a predetermined temperature. The thirdvalve is in the second position when the temperature of the firstcoolant sensed by the temperature sensor is at or below thepredetermined temperature. The predetermined temperature is atemperature at which the first coolant is to be supplied to the at leastone air-to-liquid heat exchanger.

In an additional aspect, at least one of the second valve and the thirdvalve is in the first position when the temperature of the first coolantsensed by the temperature sensor is above the predetermined temperature.

In a further aspect, for an equivalent flow rate of the first coolant,one of the second valve and the third valve is in the first positionwhen the temperature of the first coolant sensed by the temperaturesensor is above the predetermined temperature by a first amount, andboth of the second valve and the third valve are in the first positionwhen the temperature of the first coolant sensed by the temperaturesensor is above the predetermined temperature by a second amount, thesecond amount being greater than the first amount.

In an additional aspect, the predetermined temperature is between 8degrees Celsius and 18 degrees Celsius.

In a further aspect, the at least one first pump is fluidly connectedbetween the at least one air-to-liquid heat exchanger and theliquid-to-liquid heat exchanger.

In an additional aspect, the at least one air-to-liquid heat exchangeris a plurality of air-to-liquid heat exchangers fluidly connected inparallel.

In a further aspect, the at least one air-to-liquid heat exchanger is atleast one coil.

In an additional aspect, the liquid-to-liquid heat exchanger is acounterflow plate-type heat exchanger.

In a further aspect, the first coolant is at least one of water andantifreeze.

In an additional aspect, a temperature of the first coolant supplied tothe at least one air-to-liquid heat exchanger is substantially constant.

In a further aspect, the temperature of the first coolant supplied tothe at least one air-to-liquid heat exchanger is between 8 degreesCelsius and 18 degrees Celsius.

In an additional aspect, a temperature of the first coolant downstreamof the at least one air-to-liquid heat exchanger and upstream of theliquid-to-liquid heat exchanger is at least 18 degrees Celsius.

In a further aspect, a temperature of the first coolant downstream ofthe at least one air-to-liquid heat exchanger and upstream of theliquid-to-liquid heat exchanger is at least 18 degrees Celsius.

In an additional aspect, the temperature of the first coolant downstreamof the at least one air-to-liquid heat exchanger and upstream of theliquid-to-liquid heat exchanger is at least 22 degrees Celsius.

In another aspect, the present provides a data center having a roomhaving a cold aisle and a hot aisle, a plurality of electroniccomponents disposed between the cold aisle and the hot aisle, air in theroom circulating through the plurality of electronic components from thecold aisle to the hot aisle, the data center cooling system describedabove, the at least one air-to-liquid heat exchanger being disposedbetween the hot aisle and the cold aisle, and at least one fancirculating air through the at least one air-to-liquid heat exchangerfrom the hot aisle to the cold aisle.

In a further aspect, a temperature of the hot aisle is between 26degrees Celsius and 38 degrees Celsius and a temperature of the coldaisle is between 15 degrees Celsius and 25 degrees Celsius.

In an additional aspect, the at least one fan is at least one first fanand an air supply system is fluidly connected to the room for supplyingair from outside the room to the room. The air supply system includes anair filter, and a second fan supplying air from outside the room to theroom.

For purposes of this application, the term “free cooling unit” means aunit that makes use of external air temperatures to cool water or othercoolant. It should be understood that the “free cooling” obtained fromthe free cooling unit is not entirely free since at least one pumptypically needs to be used to run the water or other coolant through thefree cooling unit and since at least one fan is typically used to directand increase the flow rate of external air through the free coolingunit. Examples of free cooling units include, but are not limited to,cooling towers and dry coolers.

Embodiments of the present invention each have at least one of theabove-mentioned object and/or aspects, but do not necessarily have allof them. It should be understood that some aspects of the presentinvention that have resulted from attempting to attain theabove-mentioned object may not satisfy this object and/or may satisfyother objects not specifically recited herein.

Additional and/or alternative features, aspects, and advantages ofembodiments of the present invention will become apparent from thefollowing description, the accompanying drawings, and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, as well as otheraspects and further features thereof, reference is made to the followingdescription which is to be used in conjunction with the accompanyingdrawings, where:

FIG. 1 is a schematic side elevation view of a section of data centerhaving a cooling system;

FIG. 2 is a perspective view of a rack of the data center of FIG. 1 withelectronic components stored in the rack;

FIG. 3 is a schematic representation of the coolant cooling system ofthe data center of FIG. 1;

FIG. 4 is a schematic representation of a chiller of the coolant coolingsystem of FIG. 3;

FIG. 5 is a schematic representation of a cooling tower of the coolantcooling system of FIG. 3;

FIG. 6 is a schematic representation of a dry cooler that can be used inthe coolant cooling system of FIG. 3 as an alternative to the coolingtower of FIG. 5;

FIG. 7 is a schematic representation of an outside air supply system ofthe data center of FIG. 1; and

FIG. 8 is a schematic representation of an alternative embodiment of anoutside air supply system of the data center of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates a data center 2 including a data center room 4containing a number of electronic equipment racks 6, a coolant coolingsystem 8, and an outside air supply system 10.

In this embodiment, the racks 6 are arranged to form rings of racks 6over various levels. It is contemplated that instead of being arrangedto form rings, the racks 6 on each level could be arranged to form asquare, hexagon, octagon each having one or more racks 6 per side or anyother configuration that the room 4 will accommodate. Although only sixracks 6 disposed in three levels are shown in the room 4 for ease ofillustration, it should be understood that it is contemplated that theroom 4 could contain hundreds of such racks disposed over more thanthree levels. It is contemplated that the room 4 could be of any othershape. For example, it is contemplated that the room 4 could have arectangular or circular cross-section. It is contemplated that in anembodiment where the room 4 has a rectangular cross-section, the racks 6could be disposed over a single level such that FIG. 1 would illustratea plan view of such a room. It is also contemplated that the room 4could have a single row of racks 6, in which case the racks 6 wouldseparate the room into two aisles. Other configurations of the racks 6inside a room 4 are contemplated. It is contemplated that floors and/orbridges (not shown) could be provided between each level of racks 6 tofacilitate access to the racks 6. The floors and bridges should howeverhave a lattice structure, a grill structure or any other structuredefining apertures therein such that the flow of air from one level ofracks 6 to the other is not impeded too much by the presence of thefloors and bridges.

Partitions 12 are disposed between each level of racks 6. Otherpartitions (not shown) are also disposed between adjacent racks 6 of asame level. The partitions and the racks 6 thus form a central aisle 14and an outer aisle 16 inside the room 4. It is contemplated that one ormore of the partitions could be provided with a door to provide accessto the central aisle 14.

FIG. 2 schematically illustrates one possible embodiment of a rack 6.The rack 6 includes a frame 18 having a number of brackets and/orshelves (not shown) supporting electronic components 20 thereon. Theelectronic components 20 include, but are not limited to, general orspecial purpose computers, servers, electronic data storage,telecommunication devices, and combinations thereof. Although the frame18 shown in FIG. 2 has four open sides, it is contemplated that theframe 18 could have only two open sides, such that when the rack 6 isinstalled in the room 4, one side faces the central aisle 14 and theother side faces the outer aisle 16. At least some of the electroniccomponents 20 are provided with fans (not shown) used to create a flowof air over at least some of the hardware in these components 20 so asto remove heat therefrom. The electronic components 20 having fans arearranged in the racks 6 such that the fans take air from the outer aisle16 and blow it in the central aisle 14.

Returning to FIG. 1, a fan 22 is disposed near a bottom of the centralaisle 14. It is contemplated that more than one fan 22 could beprovided. The fan 22 is an axial fan, but it is contemplated that othertypes of fans could be used. The fan 22 takes air in the central aisle14 and pushes the air through air-to-liquid heat exchangers 24. The heatexchangers 24 are arranged in a configuration similar to that of theracks 6, but it is contemplated that they could be disposed in adifferent configuration. In an exemplary embodiment, the heat exchangers24 are cooling coils, but it is contemplated that other types ofair-to-liquid heat exchangers 24 could be used. As will be explained ingreater detail below, as the air flows through the heat exchangers 24,heat from the air is transferred to the coolant flowing in the heatexchangers 24. As a result the air is cooled. The cool air then flowsupwardly in the outer aisle 16. As will be described below, the speed ofthe fan 22 is controlled such that the air pressure in the outer aisle16 is slightly higher than the air pressure in the central aisle, and asa result, the cool air flows from the outer aisle 16 to the centralaisle 14 through the racks 6 and the electronic components 20. As itflows through the racks 6 and the electronic components 20, the heatgenerated by the hardware of the electronic components 20 is transferredto the air. As a result, the electronic components 20 are cooled. Forelectronic components 20 provided with fans, the fans are used toincrease the flow of air over their associated hardware and thereforeincrease the rate of heat transfer from the hardware to the air, thusassisting in efficient operation of the electronic components 20 andhelping to prevent the failure of the electronic components 20 due tooverheating. It is contemplated that such fans could be used only whenthe temperature of the hardware exceeds a predetermined temperature. Itis contemplated that fans could be mounted to the racks 6 to increasethe flow of air therethrough. The air entering the central aisle 14after passing through the racks 6 and the electronic components 20 istherefore warmer than the air in the outer aisle 16. For this reason,the central aisle 14 and the outer aisle 16 will also be referred toherein as the hot aisle 14 and the cold aisle 16 respectively. The fan22 continuously recirculates the air from the hot aisle 14, through theheat exchangers 24, to the cold aisle 16, through the racks 6 and theelectronic components 20, and back to the hot aisle 14 as describedabove. It is contemplated that instead of having a fan 22 disposed inthe hot aisle 14 that pushes the air from the hot aisle 14 through theheat exchangers 24, that fans could be provided in the cold aisle 16that would pull the air from the hot aisle 14 through the racks 6 andthe electronic components 20.

In an exemplary embodiment, the heat exchangers 24 are designed suchthat at full capacity of the room 4 (i.e. a room filled with the maximumnumber of operating electronic components for which it has beendesigned) air entering the heat exchangers 24 at a temperature between26 and 38 degrees Celsius from the hot aisle 14 leaves the heatexchangers 24 at a temperature between 15 and 25 degrees Celsius. Inanother exemplary embodiment, the speed of the fan 22 and of the coolantflowing through the heat exchangers 24 are controlled such that thetemperatures in the hot and cold aisles 14, 16 are maintained at or near(i.e. plus or minus 0.5 degrees Celsius) predetermined temperatureswithin the above-mentioned ranges.

One or more temperature sensors 26 and one or more air pressure sensors28 are provided in the hot aisle 14. Similarly, one or more temperaturesensors 30 and one or more air pressure sensors 32 are provided in thecold aisle 16. These are used to control the temperature and pressure inthe hot and cold aisles 14, 16. The temperature and pressure in the hotand cold aisles 14, 16 can fluctuate, for example, as electroniccomponents 20 are turned on and off, based on fluctuating levels ofpower supplied to the electronic components 20, due to the addition andremoval of electronic components 20 in the room 4 which increases orreduces the amount of heat generated in the room 4, due to aperturesbeing formed or blocked between the hot and cold aisles 14, 16 as aresult of the addition and removal of electronic components 20 in racks6 which affects the flow of air between the hot and cold aisles 14, 16,and by the opening and closing of doors between the hot and cold aisles14, 16 or to access the room 4.

In order to control the temperature in the hot aisle 14, a control unit(not shown) controls the speed of the fan 22 based on the readingsobtained from the temperature sensor(s) 26 and the air pressure sensors28 and 32. If it is determined that the temperature in the hot aisle 14is below the desired temperature, the speed of the fan 22 is decreasedsuch that the air pressure in the cold aisle 16 is decreased relative tothe air pressure in the hot aisle 14, thus lowering the speed of the airflowing through the racks 6 and the electronic components 22. However,the air pressure in the cold aisle 16 should not be lowered below theair pressure in the hot aisle 14, which would cause the air to flowthrough the racks 6 and electronic components 20 from the hot aisle 14to the cold aisle 16. When the air pressure in the cold aisle 14 is thesame as the air pressure in the hot aisle 16, the flow of air throughthe electronic components 20 is generated by the fans of the electroniccomponents 20 provided with such fans. If it is determined that thetemperature in the hot aisle 14 is above the desired temperature, thespeed of the fan 22 is increased such that the air pressure in the coldaisle 16 is increased relative to the air pressure in the hot aisle 14,thus increasing the speed of the air flowing through the racks 6 and theelectronic components 20. However, it is contemplated that control unitcould prevent the air pressure in the cold aisle 16 to exceed apredetermined pressure difference with the hot aisle 14. In an exemplaryembodiment, the speed of the fan 22 is controlled such that the airpressure in the cold aisle 16 is between 0 and 50 Pascal above the airpressure in the hot aisle 14.

In order to control the temperature in the cold aisle 16, the controlunit mentioned above or a different control unit controls the flow rateof coolant in the heat exchangers 24 via a valve (not shown) based onthe readings obtained from the temperature sensor(s) 30. As will beexplained below, a temperature of the coolant entering the heatexchangers 24 is controlled to be substantially constant. If it isdetermined that the temperature in the cold aisle 16 is below thedesired temperature, the flow rate of coolant in the heat exchangers 24is reduced. If it is determined that the temperature in the cold aisle16 is above the desired temperature, the flow rate of coolant in theheat exchangers 24 is increased.

In an alternative embodiment, it is contemplated that the temperature inthe cold aisle 16 can be controlled by controlling a temperature of thecoolant entering the heat exchangers 24. If it is determined that thetemperature in the cold aisle 16 is below the desired temperature, thetemperature of the coolant supplied to the heat exchangers 24 isincreased. If it is determined that the temperature in the cold aisle 16is above the desired temperature, the temperature of the coolant insupplied to the heat exchangers 24 is decreased.

For reasons explained below, the heat exchangers 24 are filterless (i.e.not provided with air filters). As such, the fan 22 can operate at lowerspeeds than would otherwise be required had air filters been providedupstream or downstream of the heat exchangers since the fan 22 does notneed to compensate for the head loss that the air filters would havecaused. These lower fan speeds can result in substantial power savings.The coolant used in the heat exchangers 24 is water. However, it iscontemplated that other types of coolant could be used such as, forexample, antifreeze or a water-antifreeze solution. One example ofantifreeze is glycol, but it is contemplated that other antifreezescould be used. The heat exchangers 24 are connected in parallel to thecoolant cooling system 8. The heat exchangers 24 and the coolant coolingsystem 8 together form a cooling system of the data center 2. The hotcoolant leaving the heat exchangers 24 enters the coolant cooling system8 where it is cooled as will be described in greater detail below and isthen returned to the heat exchangers 24. It is contemplated that thesame coolant cooling system 8 could be used to cool the coolant used inthe heat exchangers 24 of more than one data center room 4 by connectingthe heat exchangers 24 in parallel to the coolant cooling system 8. Itis also contemplated that multiple coolant cooling systems 8 could beconnected in parallel with each other.

As would be appreciated, it is difficult to build a perfectly air tightroom. The connection between the structural components of the room, theapertures formed in the structure for running wires into and out of theroom (power, telecommunication, etc.) and doors to provide access to theroom are all examples of reasons which makes this difficult. Therefore,air outside a room which is not air tight could enter the room andaffect the temperature, pressure and humidity level in the room andcould carry dust with it. As would be understood, this would affect theefficiency of the room. To overcome this, the air pressure inside thedata center room 4 as determined by the air pressure sensors 28, 32 ismaintained slightly above the air pressure outside of the room 4 asdetermined by an air pressure sensor (not shown) disposed outside of theroom 4. This causes a slight flow of air out of the room 4 whichprevents the entry of outside air and dust. To make up for this loss ofair inside the room 4 and to maintain the pressure inside the room 4,the air supply system 10 continuously supplies air from outside the room4 into the room 4. As will be described in greater detail below, the airsupply system 10 conditions the outside air prior to supplying it to theroom 4.

Turning now to FIG. 3, the coolant cooling system 8 will be described inmore detail. Although, as explained above, it is contemplated thatvarious types of coolant could be used, the coolant cooling system 8will be described for water being used as the coolant. The coolantcooling system 8 supplies the water to the heat exchangers 24 at asubstantially constant (i.e. plus or minus 0.5 degrees Celsius)predetermined temperature. In an exemplary embodiment, thispredetermined temperature is between 8 and 18 degrees Celsius. This ishigher than the temperature of 7 degrees Celsius typically found inthese types of applications. The temperature of the water being returnedto the coolant cooling system 8 from the heat exchangers 24 will dependon the temperature of the water entering the heat exchangers 24, thedesign of the heat exchangers 24, the flow rate of water through theheat exchangers 24, the temperature of the hot and cold aisles 14, 16,and the speed of the fan 22. In an exemplary embodiment, the temperatureof the water being returned to the coolant cooling system 8 from theheat exchangers 24 is at least 18 degrees Celsius. In another exemplaryembodiment, this temperature is at least 22 degrees Celsius. This ishigher than the temperature of 12.2 degrees Celsius typically found inthese types of applications.

By using heat exchangers 24 having higher entry and exit coolanttemperatures than typically used in this type of application (i.e. datacenter cooling) it has been found that the efficiency of the data centercooling system can be improved. Combining this with the slower fan speedpossible by eliminating the air filters in the room 4 further increasesthe efficiency.

As can be seen in FIG. 3, water entering the coolant cooling system 8first flows through a pump 34. The pump 34 pumps the water from the heatexchangers 24, causes it to flow through the coolant cooling system 8,and through the heat exchangers. It is contemplated that more than onepump 34 could be provided. It is also contemplated that the pump 34could be provided elsewhere between the outlets of the heat exchangers24 and the inlets of the heat exchangers 24. A temperature sensor 36senses a temperature of the water exiting the pump 34. A flow meter 38senses the flow rate of the water exiting the pump 34. It iscontemplated that the flow meter 38 could be disposed upstream of thetemperature sensor 36.

From the flow meter 38, the water selectively flows through aliquid-to-liquid heat exchanger 40 to be cooled. In the presentembodiment, the heat exchanger 40 is a counterflow plate-type heatexchanger. It is contemplated that other types of liquid-to-liquid heatexchangers could be used, such as a shell and tube heat exchanger. Aswill be explained in greater detail below, the coolant used to cool thewater flowing from the flow meter 38 is water supplied from a freecooling unit in the form of cooling tower 42. It is contemplated thatwhen the coolant used in the heat exchangers 24 and the coolant used inthe free cooling unit are the same, that the liquid-to-liquid heatexchanger could be a hydraulic bridge inside which both of the coolantflows are mixed. It is also contemplated that more than oneliquid-to-liquid heat exchanger 40 could be provided. It is contemplatedthat more than one free cooling unit, such as cooling tower 42, could beprovided. A valve 44 can be opened to permit a majority of the waterflowing from the flow meter 38 to bypass the heat exchanger 40 forreasons described below. It is contemplated that the valve 44 could bereplaced by a three-way valve such that all of the water flowing fromthe flow meter 38 flows through the heat exchanger 40 or bypasses theheat exchanger 40.

A temperature sensor 46 senses the temperature of the water exiting theheat exchanger 40 and/or the valve 44. From the heat exchanger 40 and/orthe valve 44, the water selectively flows through a chiller 48 connectedin series with the heat exchanger 40. The chiller 48 is avapor-compression chiller, however it is contemplated that other typesof chillers could be used. It is contemplated that more than one chiller48 could be provided.

As can be seen in FIG. 4, the chiller 48 includes an evaporator 50through which water from the heat exchanger 40 and/or the valve 44flows, a condenser 52 through which water from the cooling tower 42flows, a refrigerant loop 54 inside which a refrigerant flows, acompressor 56 fluidly connected to the refrigerant loop 54, a motor 58driving the compressor 56, and a throttle valve 60 fluidly connected tothe refrigerant loop 54. The refrigerant enters the compressor 56 as asaturated vapor. The compressor 56 compresses this refrigerant vapor,thereby increasing its temperature. This refrigerant vapor then flowsthrough the condenser 52. In the condenser 52, the water from thecooling tower 52 absorbs heat from the refrigerant, causing it to cooland condense into a liquid. The liquid refrigerant then flows throughthe throttle valve 60. This causes the refrigerant to experience asudden drop in pressure that causes a portion of the liquid refrigerantto flash evaporate. This lowers the temperature of the liquid and vaporrefrigerant mixture below the temperature of the water entering theevaporator 50. This refrigerant mixture then flows through theevaporator 50 and absorbs heat from the water flowing in the evaporator50. This causes the liquid portion of the refrigerant mixture toevaporate and the temperature of the water to be reduced. Therefrigerant then flows back through the compressor 56 and the cycle isrepeated. The chiller 48 is provided with temperature sensors (notshown) sensing the entry and exit temperatures of the water flowingthrough the evaporator 50 and through the condenser 52. It iscontemplated that these temperature sensors could be provided externallyof the chiller 48.

As can be seen in FIG. 3, a valve 62 can be opened to permit a majorityof the water flowing from the heat exchanger 40 and/or the valve 44 tobypass the chiller 48 for reasons described below. It is contemplatedthat the valve 62 could be replaced by a three-way valve such that allof the water flowing from the heat exchanger 40 and/or the valve 44flows either through the chiller 48 or bypasses the chiller 48.

From the chiller 48 and/or the valve 62, the water selectively flowsthrough a chiller 64 connected in series with the chiller 48. Thechiller 64 is a vapor-compression chiller of the same type and coolingcapacity as the chiller 48. As such the chiller 64 operates in the samemanner as the chiller 48 and its operation will therefore not bedescribed herein. It is contemplated that the chiller 64 could be of adifferent type and/or have a different cooling capacity than the chiller48. It is also contemplated that more than one chiller 64 could beprovided. A valve 66 can be opened to permit a majority of the waterflowing from the chiller 48 and/or the valve 62 to bypass the chiller 64for reasons described below. It is contemplated that the valve 66 couldbe replaced by a three-way valve such that all of the water flowing fromthe chiller 48 and/or the valve 62 flows either through the chiller 64or bypasses the chiller 64.

From the chiller 64 and/or the valve 66, the cooled water is returned tothe heat exchangers 24 to cool the air in the room 4 as described above.A temperature sensor 67 senses the temperature of the water supplied tothe heat exchangers 24.

Turning now to FIG. 5, the cooling tower 42 will be described. In thisfigure, the flow of water is illustrated by black arrows and the flow ofair by white arrows. The cooling tower 42 is an open circuit, induceddraft, counterflow cooling tower. It is contemplated that other types ofcooling towers could be used. The cooling tower 42 has a fan 68 at a topthereof that draws outside air into the cooling tower 42 near a bottomthereof and causes it to flow upwardly through the cooling tower 42. Itis contemplated that more than one fan 68 could be used. Water to becooled by the cooling tower 42 is supplied to a pipe 70 near a top ofthe cooling tower 42. Nozzles 72 connected to the pipe 70 spray thewater inside the cooling tower 42. The sprayed water flows down in thecooling tower 42 by gravity. As the sprayed water flows against the flowof air in the cooling tower 42, a portion of the water evaporates,thereby reducing the temperature of the remaining water. To increase thecontact surface between the water and the air and the time of contactbetween the two in order to increase the cooling of the water, thesprayed water flows over fill material 74. It is contemplated that thefill material 74 could be omitted. The cooled water collects in a basin76 at the bottom of the cooling tower 42. The temperature of the watercollecting in the basin 76 depends on the temperature and humidity ofthe air flowing in the cooling tower 42 and the temperature of the waterentering the cooling tower 42 to be cooled. From the basin 76, thecooled water flows in the coolant cooling system as described below.Since a certain amount of water evaporates during the cooling process, awater supply system (not shown) is provided to add water in the basin 76(or at any other point in the cooling tower 42 or its associated watercircuit) to make up for the evaporated water.

A pump 78 pumps the water from the basin 76 of the cooling tower 42 andcauses it to flow through the circuit described below and to return tothe pipe 70 of the cooling tower 42. It is contemplated that the pump 78could be provided elsewhere along the circuit described below. It isalso contemplated that more than one pump 78 could be provided. Atemperature sensor 80 senses a temperature of the water exiting the pump78. From the pump 78, the water flows through the heat exchanger 40 tocool the water coming from the heat exchangers 24 or bypasses the heatexchanger 40 depending on a position of a three-way valve 82. When thetemperature sensed by the temperature sensor 80 is below the temperaturesensed by the temperature sensor 36 by at least a predetermined amount,the valve 82 is positioned such that water flowing from the pump 78flows through the heat exchanger 40 and the valve 44 is closed such thatwater flowing from the pump 34 also flows through the heat exchanger 40.As a result, water flowing from the pump 34 is cooled by the waterflowing from the cooling tower 42. In an exemplary embodiment, thetemperature sensed by the temperature sensor 80 has to be between 0.1and 10 degrees below the temperature sensed by the temperature sensor 36for the heat exchanger 40 to be used to cool the water flowing from thepump 34 as described above. However it is contemplated that this amountcould be higher than 10 degrees. When the temperature sensed by thetemperature sensor 80 is above the temperature sensed by the temperaturesensor 36 or below the temperature sensed by the temperature sensor 36by less than the predetermined amount, the valve 82 is positioned suchthat water from the pump 78 bypasses the heat exchanger 40 and the valve44 is opened such that a majority of water from the heat exchanger 24also flows through the heat exchanger 40.

From the valve 82, the water selectively flows through the chiller 64 tocool the refrigerant therein. A valve 84 can be opened to permit amajority of the water flowing from the valve 82 to bypass the chiller 64for reasons described below. It is contemplated that the valve 84 couldbe replaced by a three-way valve such that all of the water flowing fromthe valve 82 flows either through the chiller 64 or bypasses the chiller64. When the chiller 64 is to be used to cool the water used in the heatexchangers 24, both of the valves 66 and 84 are closed and the motor ofthe chiller 64 is turned on. Otherwise, both of the valves 66 and 84 areopened and the motor of the chiller 64 is turned off.

From the chiller 64 and/or valve 84, the water selectively flows throughthe chiller 48 to cool the refrigerant therein. A valve 86 can be openedto permit a majority of the water flowing from the chiller 64 and/orvalve 84 to bypass the chiller 48 for reasons described below. It iscontemplated that the valve 86 could be replaced by a three-way valvesuch that all of the water flowing from the chiller 64 and/or valve 84flows either through the chiller 48 or bypasses the chiller 48. When thechiller 48 is to be used to cool the water used in the heat exchangers24, both of the valves 62 and 86 are closed and the motor 58 of thechiller 48 is turned on. Otherwise, both of the valves 62 and 86 areopened and the motor 58 of the chiller 48 is turned off.

From the chiller 48 and/or valve 86, the water flows to the pipe 70 ofthe cooling tower 42 to be cooled and recirculated through the circuitdescribed above.

It is contemplated that the cooling tower 42 could be replaced by a drycooler 88, such as the one shown in FIG. 6. The dry cooler 88 includesan air-to-liquid heat exchanger 90 disposed outside and through which acoolant to be cooled flows. A pair of fans 92 induces a flow of ambientair over the heat exchanger 90 to cool the coolant flowing therein. Itis contemplated that only one or more than two fans 92 could be used. Ifthe data center 2 is installed in a region where the temperaturetypically remains above 0 degree Celsius, water can be used as thecoolant in the dry cooler 88. Otherwise, a coolant having a lowerfreezing temperature, such as antifreeze or a water-antifreeze solution,should be used. From the heat exchanger 90 of the dry cooler 88, thecoolant flows through the same circuit as the water from the coolingtower 42 described above. It is contemplated that the cooling tower 42could also be replaced by other types of free cooling units.

Although some temperature sensors and a flow meter have been describedabove, it is contemplated that the coolant cooling system 8 could beprovided with additional temperature sensors and flow meters that couldbe used in controlling the coolant cooling system 8 and/or to monitorthe operation of the coolant cooling system 8.

When the temperature of the water sensed by the temperature sensor 46corresponds, within a certain tolerance level, to the predeterminedtemperature at which the water is to be supplied to the heat exchangers24 as a result of the cooling thereof by the heat exchanger 40, thechillers 48 and 64 do not need to be used. As such all of the valves 62,66, 84 and 86 are opened.

When the temperature of the water sensed by the temperature sensor 46 isless than the predetermined temperature at which the water is to besupplied to the heat exchangers 24 as a result of the cooling thereof bythe heat exchanger 40, the speed of the fan 68 of the cooling tower 42and/or the speed of the pump 78 is/are adjusted in order to increase thetemperature of the water exiting the heat exchanger 40 and sensed by thetemperature sensor 46 to the predetermined temperature. Alternatively,it is contemplated that the valve 44 could be partially opened such thata temperature of the water resulting from the mix of water flowingthrough the heat exchanger 40 and of water bypassing the heat exchanger40 corresponds to the predetermined temperature. Under such conditions,the chillers 48 and 64 do not need to be used and the valves 62, 66, 84and 86 are opened.

When the temperature of the water sensed by the temperature sensor 46 isabove the predetermined temperature at which the water is to be suppliedto the heat exchangers 24 either as a result of insufficient coolingthereof by the heat exchanger 40 or as a result of the water bypassingthe heat exchanger 40, it is first determined if only one or both of thechillers 48 and 64 are needed to reduce the temperature of the water tothe predetermined temperature before it is supplied to the heatexchangers 24. This is done based at least in part on the differencebetween the temperature sensed by the temperature sensor 46 and thepredetermined temperature at which the water is to be supplied to theheat exchangers and by the flow rate of the water as sensed by the flowmeter 38.

If it is determined that both chillers 48 and 64 are to be used, all ofthe valves 62, 66, 84 and 86 are closed. In an exemplary embodiment,each one of the chillers 48 and 64 is controlled so as to reduce thetemperature of the water by half of what is needed to bring it to thepredetermined temperature at which it is to be supplied to the heatexchangers 24. For example, when the temperature sensor 46 senses awater temperature of 12 degrees above the predetermined temperature atwhich the water is to be supplied to the heat exchangers 24, the chiller48 is controlled to reduce the water temperature by 6 degrees and thechiller 64 is controlled to reduce the water temperature by 6 degrees.

If it is determined that only one of the chillers 48 and 64 is to beused, then the one of the chillers 48 and 64 which can reduce thetemperature of the water most efficiently is used. This is usually thechiller 48, in which case the valves 62 and 86 are closed and the valves66 and 84 are opened. However it is contemplated that under certainconditions, the chiller 64 could be the one that is used, in which casethe valves 66 and 84 are closed and the valves 62 and 86 are opened.

In an exemplary embodiment, it is determined that only one of thechillers 48 and 64 can be used only if the temperature of the water canbe reduced to the predetermined temperature by one of the chillers 48and 64 operating at a fraction of its maximum cooling capacity.Otherwise, both chillers 48 and 64 are used.

If the temperature of the water sensed by the temperature sensor 67 isoutside a narrow range above or below the predetermined temperature atwhich water is to be supplied to the heat exchangers 24, the operationof the heat exchanger 40 and of the chillers 48 and 64 is adjustedaccordingly.

Turning now to FIG. 7, the outside air supply system 10 will bedescribed in more detail. Outside air entering the air supply system 10first flows through an air filter 100 to remove a larger percentage ofdust and particles that could be present in the air. It is contemplatedthat more than one air filter 100 could be provided. Since the airsupplied by the air supply system 10 is filtered and pressurizes theroom 4 above the air pressure outside the room 4, air filters are notnecessary inside the room 4 to filter the air being circulated therein,thus allowing the fan 22 to operate at lower speeds thereby increasingthe efficiency of the data center 2. From the air filter 100, the airflows through an air-to-liquid heat exchanger 102 used to cool or heatthe air as described below. The heat exchanger 102 is a coil, but it iscontemplated that other types of heat exchangers could be used. From theheat exchanger 102, the air flows through another air-to-coolant heatexchanger 104 used to dehumidify and further cool the air if needed asdescribed below. The heat exchanger 104 is a coil, but it iscontemplated that other types of heat exchangers could be used. Thecoolant flowing through the heat exchanger 104 when it is in operationis cooled by an autonomous refrigeration system 106. The coolant flowingthrough the heat exchanger 104 is a liquid such as water, an antifreeze,or a solution thereof. As such the air-to-coolant heat exchanger 104 isan air-to-liquid heat exchanger 104. It is contemplated that the coolantflowing through the heat exchanger 104 could be a refrigerant, in whichcase the air-to-coolant heat exchanger 104 would be anair-to-refrigerant heat exchanger 104. A fan 108 is disposed near theoutlet of the air supply system 10. The fan 108 is an axial fan, but itis contemplated that another type of fan, such as a centrifugal fan or amixed flow fan, could be used. The fan 108 pulls the air through the airsupply system 10 and pushes it inside the room 4. In an exemplaryembodiment, the air supply system 10 supplies the air to the cold aisle16. The flow rate of air generated by the fan 108 is lower than the flowrate of air generated by the fan 22. In an exemplary embodiment, theflow rate generated by the fan 108 is between 0.1% and 25% of the flowrate generated by the fan 22. In another exemplary embodiment, the flowrate generated by the fan 108 is between 2% and 5% of the flow rategenerated by the fan 22. It is contemplated that the fan 108 and thefilter 100 could be disposed elsewhere along the air supply system 10.For example, the fan 108 could be disposed at the inlet of the airsupply system 10 and the filter 100 near the outlet of the air supplysystem.

The heat exchanger 102 has a water-glycol solution circulatedtherethrough by a pump 110. It is contemplated that a coolant other thana water-glycol solution could be used such as another antifreeze. It iscontemplated that more than one pump 110 could be provided. Thewater-glycol solution also flows through a counterflow plate-type heatexchanger 112 where it is heated or cooled depending on whether theoutside air is to be heated or cooled as will be described below. It iscontemplated that the heat exchanger 112 could be a different type ofliquid-to-liquid heat exchanger, such as, for example, a shell and tubeheat exchanger.

The liquid used to heat or cool the water-glycol solution in the heatexchanger 112 is water from the coolant cooling system that is used inthe heat exchangers 24. As can be seen in FIG. 3, a three-way valve 114has a first port connected upstream of the valve 34 to receive hot waterfrom the heat exchangers 24, a second port connected downstream of thechiller 64 and the valve 66 to receive cool water therefrom, and a thirdport connected to a pump 116. When the water-glycol solution is to beheated in the heat exchanger 112, the valve 114 is positioned so as tosupply hot water to the pump 116 which then pumps it through the heatexchanger 112. When the water-glycol solution is to be cooled in theheat exchanger 112, the valve 114 is positioned so as to supply coolwater to the pump 116 which then pumps it through the heat exchanger112. From the heat exchanger 112, the water pumped by the pump 116 issupplied to a three-way valve 118. When the water supplied to the pump116 is hot water, the valve 118 is positioned to supply the waterreturning from the heat exchanger 112 upstream of the pump 34 as shown.When the water supplied to the pump 116 is cool water, the valve 118 ispositioned to supply the water returning from the heat exchanger 112downstream of the chiller 64 and the valve 66 as shown.

Although not shown, temperature sensors are provided in the air supplysystem 10 to sense the temperature of the outside air, of the airflowing out of the heat exchanger 102 and of the air flowing out of theheat exchanger 104. The temperature of the air supplied to the room 4 bythe air supply system 10 is controlled by the air supply system so as tobe above 0 degree Celsius, to prevent freezing, but below thetemperature of the cold aisle 16 as sensed by the temperature sensor(s)30 in order to prevent water condensation inside the room 4.

When the temperature of the outside air is too low, the water-glycolsolution flowing through the heat exchanger 102 is heated as indicatedabove. The air flowing through the heat exchanger 102 is thereforeheated. The speed of the pump 110 and/or of the pump 116 is controlledsuch that the temperature of the air downstream of the heat exchanger102 is within the desired range to be supplied to the room 4. Therefrigeration system 106 is turned off since under these conditions theheat exchanger 104 is not needed to cool the air.

When the temperature of the outside air is too high, the refrigerationsystem 106 is turned on and controlled such that the heat exchanger 104cools the air flowing therethrough. If the resulting temperature of theair downstream of the heat exchanger 104 is within the desired range tobe supplied to the room 4, then the pump 110 is turned off since theheat exchanger 102 is not needed to cool the air. If the resultingtemperature of the air downstream of the heat exchanger 104 is stillabove the desired range to be supplied to the room 4, then the pump 110is turned on and the water-glycol solution flowing through the heatexchanger 102 is cooled as indicated above. The air flowing through theheat exchanger 102 is therefore cooled. The speed of the pump 110 and/orof the pump 116 is controlled such that the temperature of the airflowing through the heat exchanger 102 is reduced efficiently. Therefrigeration system 106 is controlled such that the heat exchanger 104cools the air flowing therethrough to a temperature within the desiredrange to be supplied to the room 4. When in operation, the heatexchanger 104 also dehumidifies the air flowing therethrough.

It is contemplated that if the data center 2 is installed in a regionwhere the temperature typically remains above 0 degree Celsius, that thewater-glycol solution loop, pump 110 and heat exchanger 112 of the airsupply system 10 could be omitted and that the hot or cool watersupplied by the pump 116 could be supplied directly to the heatexchanger 102 as in the air supply system 10′ shown in FIG. 8. The otherelements of the air supply system 10′ are the same as those of the airsupply system 10, as such they have been labelled with the samereference numerals and will not be described again.

Modifications and improvements to the above-described embodiments of thepresent invention may become apparent to those skilled in the art. Theforegoing description is intended to be exemplary rather than limiting.The scope of the present invention is therefore intended to be limitedsolely by the scope of the appended claims.

What is claimed is:
 1. A data center comprising: a room having a coldaisle and a hot aisle; a plurality of electronic components disposedbetween the cold aisle and the hot aisle, air in the room circulatingthrough the plurality of electronic components from the cold aisle tothe hot aisle; at least one air-to-liquid heat exchanger disposedbetween the hot aisle and the cold aisle; at least one first fancirculating air in the room at a first flow rate, the at least one firstfan circulating air through the at least one air-to-liquid heatexchanger from the hot aisle to the cold aisle; and an air supply systemfluidly connected to the room for supplying air from outside the room tothe room, the air supply system including: an air filter; and a secondfan supplying air from outside the room to the room at a second flowrate, the second flow rate being lower than the first flow rate.
 2. Thedata center of claim 1, wherein the at least one air-to-liquid heatexchanger is filterless.
 3. The data center of claim 1, wherein thesecond flow rate is between 0.1% and 25% of the first flow rate.
 4. Thedata center of claim 3, wherein the second flow rate is between 2% and5% of the first flow rate.
 5. The data center of any one of claims 1 to4, wherein the at least one air-to-liquid heat exchanger is at least onefirst air-to-liquid heat exchanger; and wherein the air supply systemfurther includes at least one second air-to-liquid heat exchanger, theat least one second fan circulating air through the at least one secondair-to-liquid heat exchanger.
 6. The data center of claim 5, wherein theat least one second air-to-liquid heat exchanger selectively heats theair from the outside before the air is supplied to the room using hotcoolant exiting the at least one first air-to-liquid heat exchanger; andwherein the at least one second air-to-liquid heat exchanger selectivelycools the air from the outside before the air is supplied to the roomusing cool coolant supplied to the at least one first air-to-liquid heatexchanger.
 7. The data center of claim 6, further comprising: aliquid-to-liquid heat exchanger fluidly connected to the at least onesecond air-to-liquid heat exchanger; at least one pump circulatingcoolant between the liquid-to-liquid heat exchanger and the at least onesecond air-to-liquid heat exchanger; and at least one valve selectivelysupplying one of the hot coolant and the cool coolant to theliquid-to-liquid heat exchanger.
 8. The data center of claim 6, furthercomprising: at least one valve selectively supplying one of the hotcoolant and the cool coolant to the second air-to-liquid heat exchanger;and at least one pump circulating the one of the hot coolant and thecool coolant through the second air-to-liquid heat exchanger.
 9. Thedata center of claim 6, wherein the air supply system further includes:an air-to-coolant heat exchanger disposed downstream of at least onesecond air-to-liquid heat exchanger; and an autonomous refrigerationsystem fluidly connected to the air-to-coolant heat exchanger, theautonomous refrigeration system cooling coolant flowing through theair-to-coolant heat exchanger.
 10. The data center of claim 9, whereinthe air-to-coolant heat exchanger is a third air-to-liquid heatexchanger.
 11. The data center of claim 6, wherein the hot coolant is ata temperature of at least 18 degrees Celsius and the cool coolant is ata temperature between 8 degrees Celsius and 18 degrees Celsius.
 12. Thedata center of claim 11, wherein the coolant is at least one of waterand antifreeze.
 13. The data center of any one of claims 1 to 4, furthercomprising: at least one air temperature sensor disposed in the hotaisle for sensing an air temperature in the hot aisle; at least onefirst air pressure sensor disposed in the hot aisle for sensing an airpressure in the hot aisle; and at least one second air pressure sensordisposed in the cold aisle for sensing an air pressure in the coldaisle; wherein a speed of the at least one first fan is increased toincrease the first flow rate such that the air pressure in the coldaisle is increased relative to the hot aisle when the air temperature inthe hot aisle is above a predetermined temperature; and wherein thespeed of the at least one first fan is decreased to decrease the firstflow rate such that the air pressure in the cold aisle is decreasedrelative to the hot aisle when the air temperature in the hot aisle isbelow the predetermined temperature.
 14. The data center of claim 13,wherein the second flow rate is substantially constant.
 15. The datacenter of claim 13, wherein the predetermined temperature is between 26degrees Celsius and 38 degrees Celsius.
 16. The data center of any oneof claims 1 to 4, further comprising at least one air temperature sensordisposed in the cold aisle for sensing an air temperature in the coldaisle; wherein a flow rate of coolant in the at least one air-to-liquidheat exchanger is increased when the air temperature in the cold aisleis above a predetermined temperature; and wherein the flow rate ofcoolant in the at least one air-to-liquid heat exchanger is decreasedwhen the air temperature in the cold aisle is below the predeterminedtemperature.
 17. The data center of claim 16, wherein a temperature ofcoolant supplied to the at least one air-to-liquid heat exchanger issubstantially constant.
 18. The data center of claim 16, wherein thepredetermined temperature is between 15 degrees Celsius and 25 degreesCelsius.
 19. The data center of any one of claims 1 to 4, furthercomprising at least one air temperature sensor disposed in the coldaisle for sensing an air temperature in the cold aisle; wherein atemperature of coolant supplied to the at least one air-to-liquid heatexchanger is decreased when the air temperature in the cold aisle isabove a predetermined temperature; and wherein the temperature ofcoolant supplied to the at least one air-to-liquid heat exchanger isincreased when the air temperature in the cold aisle is below thepredetermined temperature.
 20. The data center of any one of claims 1 to4, further comprising a plurality of racks disposed between the coldaisle and the hot aisle; and wherein the plurality of electroniccomponents is disposed in the plurality of racks.
 21. A data centercooling system comprising: at least one air-to-liquid heat exchangeradapted to cool air from a hot aisle of at least one room of a datacenter; a liquid-to-liquid heat exchanger fluidly connected to the atleast one air-to-liquid heat exchanger; a first chiller fluidlyconnected to the liquid-to-liquid heat exchanger; a second chillerfluidly connected to the first chiller; at least one first pump fluidlyconnected to the at least one air-to-liquid heat exchanger for pumping afirst coolant from the at least one air-to-liquid heat exchanger, thefirst coolant flowing selectively to the liquid-to-liquid heatexchanger, and to the first and second chillers prior to flowing back tothe at least one air-to-liquid heat exchanger; a free cooling unitfluidly connected to the liquid-to-liquid heat exchanger for cooling thefirst coolant flowing therethrough and fluidly connected to the firstand second chillers for condensing refrigerant circulated therein; andat least one second pump fluidly connected to the free cooling unit forpumping a second coolant from the free cooling unit, the second coolantflowing selectively to the liquid-to-liquid heat exchanger, and to thefirst and second chillers prior to flowing back to the free coolingunit; wherein the at least one air-to-liquid heat exchanger, theliquid-to-liquid heat exchanger, the first chiller and the secondchiller are fluidly connected in series; wherein when the first coolantflows to the liquid-to-liquid heat exchanger and to the first and secondchillers, the first coolant flows sequentially from the at least oneair-to-liquid heat exchanger, to the liquid-to-liquid heat exchanger, tothe first chiller, to the second chiller, and back to the at least oneair-to-liquid heat exchanger.
 22. The data center cooling system ofclaim 21, wherein the free cooling unit, the liquid-to-liquid heatexchanger, the first chiller and the second chiller are connected inseries.
 23. The data center cooling system of claim 22, when the secondcoolant flows to the liquid-to-liquid heat exchanger and to the firstand second chillers, the second coolant flows sequentially from the freecooling unit, to the liquid-to-liquid heat exchanger, to the secondchiller, to the first chiller, and back to the free cooling unit. 24.The data center cooling system of any one of claims 21 to 23, whereinthe free cooling unit is a cooling tower; and wherein the second coolantis water.
 25. The data center cooling system of any one of claims 21 to23, wherein the free cooling unit is a dry cooler.
 26. The data centercooling system of claim 25, wherein the second coolant is at least inpart antifreeze.
 27. The data center cooling system of any one of claims21 to 23, further comprising: a first valve having a first positionwhere the second coolant flows through the liquid-to-liquid heatexchanger and a second position where at least a portion of the secondcoolant bypasses the liquid-to-liquid heat exchanger; a second valvehaving a first position where the second coolant flows through the firstchiller and a second position where at least a portion of the secondcoolant bypasses the first chiller; and a third valve having a firstposition where the second coolant flows through the second chiller and asecond position where at least a portion of the second coolant bypassesthe second chiller.
 28. The data center cooling system of any one ofclaims 21 to 23, wherein the at least one second pump is fluidlyconnected between the free cooling unit and the liquid-to-liquid heatexchanger.
 29. The data center cooling system of any one of claims 21 to23, further comprising: a first valve having a first position where thefirst coolant flows through the liquid-to-liquid heat exchanger and asecond position where at least a portion of the first coolant bypassesthe liquid-to-liquid heat exchanger; a second valve having a firstposition where the first coolant flows through the first chiller and asecond position where at least a portion of the first coolant bypassesthe first chiller; and a third valve having a first position where thefirst coolant flows through the second chiller and a second positionwhere at least a portion of the first coolant bypasses the secondchiller.
 30. The data center cooling system of claim 29, furthercomprising: a fourth valve having a first position where the secondcoolant flows through the liquid-to-liquid heat exchanger and a secondposition where at least a portion of the second coolant bypasses theliquid-to-liquid heat exchanger; a fifth valve having a first positionwhere the second coolant flows through the first chiller and a secondposition where at least a portion of the second coolant bypasses thefirst chiller; and a sixth valve having a first position where thesecond coolant flows through the second chiller and a second positionwhere at least a portion of the second coolant bypasses the secondchiller; wherein the fourth valve is in the first position when thefirst valve is in the first position, the fifth valve is in the firstposition when the second valve is in the first position, the sixth valveis in the first position when the third valve is in the first position,the fourth valve is in the second position when the first valve is inthe second position, the fifth valve is in the second position when thesecond valve is in the second position, the sixth valve is in the secondposition when the third valve is in the second position.
 31. The datacenter cooling system of claim 29, further comprising: a firsttemperature sensor sensing a temperature of the first coolant upstreamof the liquid-to-liquid heat exchanger; and a second temperature sensorsensing a temperature of the second coolant upstream of theliquid-to-liquid heat exchanger; wherein the first valve is in thesecond position at least when the temperature of the second coolantsensed by the second temperature sensor is above the temperature of thefirst coolant sensed by the first temperature sensor.
 32. The datacenter cooling system of claim 31, wherein the first valve is in thefirst position when the temperature of the second coolant sensed by thesecond temperature sensor is below the temperature of the first coolantsensed by the first temperature sensor by at least a predeterminedamount.
 33. The data center cooling system of claim 32, wherein thepredetermined amount is between 0.1 and 10 degrees.
 34. The data centercooling system of claim 29, further comprising a temperature sensorsensing a temperature of the first coolant downstream of theliquid-to-liquid heat exchanger and upstream of the first chiller; andwherein the second valve is in the second position when the temperatureof the first coolant sensed by the temperature sensor is at or below apredetermined temperature; wherein the third valve is in the secondposition when the temperature of the first coolant sensed by thetemperature sensor is at or below the predetermined temperature; whereinthe predetermined temperature is a temperature at which the firstcoolant is to be supplied to the at least one air-to-liquid heatexchanger.
 35. The data center cooling system of claim 34, wherein atleast one of the second valve and the third valve is in the firstposition when the temperature of the first coolant sensed by thetemperature sensor is above the predetermined temperature.
 36. The datacenter cooling system of claim 34, wherein, for an equivalent flow rateof the first coolant, one of the second valve and the third valve is inthe first position when the temperature of the first coolant sensed bythe temperature sensor is above the predetermined temperature by a firstamount, and both of the second valve and the third valve are in thefirst position when the temperature of the first coolant sensed by thetemperature sensor is above the predetermined temperature by a secondamount, the second amount being greater than the first amount.
 37. Thedata center cooling system of claim 34, wherein the predeterminedtemperature is between 8 degrees Celsius and 18 degrees Celsius.
 38. Thedata center cooling system of any one of claims 21 to 23, wherein the atleast one first pump is fluidly connected between the at least oneair-to-liquid heat exchanger and the liquid-to-liquid heat exchanger.39. The data center cooling system of any one of claims 21 to 23,wherein the at least one air-to-liquid heat exchanger is a plurality ofair-to-liquid heat exchangers fluidly connected in parallel.
 40. Thedata center cooling system of any one of claims 21 to 23, wherein the atleast one air-to-liquid heat exchanger is at least one coil.
 41. Thedata center cooling system of any one of claims 21 to 23, wherein theliquid-to-liquid heat exchanger is a counterflow plate-type heatexchanger.
 42. The data center cooling system of any one of claims 21 to23, wherein the first coolant is at least one of water and antifreeze.43. The data center cooling system of any one of claims 21 to 23,wherein a temperature of the first coolant supplied to the at least oneair-to-liquid heat exchanger is substantially constant.
 44. The datacenter cooling system of claim 43, wherein the temperature of the firstcoolant supplied to the at least one air-to-liquid heat exchanger isbetween 8 degrees Celsius and 18 degrees Celsius.
 45. The data centercooling system of claim 44, wherein a temperature of the first coolantdownstream of the at least one air-to-liquid heat exchanger and upstreamof the liquid-to-liquid heat exchanger is at least 18 degrees Celsius.46. The data center cooling system of any one of claims 21 to 23,wherein a temperature of the first coolant downstream of the at leastone air-to-liquid heat exchanger and upstream of the liquid-to-liquidheat exchanger is at least 18 degrees Celsius.
 47. The data centercooling system of claim 46, wherein the temperature of the first coolantdownstream of the at least one air-to-liquid heat exchanger and upstreamof the liquid-to-liquid heat exchanger is at least 22 degrees Celsius.48. A data center comprising: a room having a cold aisle and a hotaisle; a plurality of electronic components disposed between the coldaisle and the hot aisle, air in the room circulating through theplurality of electronic components from the cold aisle to the hot aisle;the data center cooling system from any one of claims 21 to 23, the atleast one air-to-liquid heat exchanger being disposed between the hotaisle and the cold aisle; and at least one fan circulating air throughthe at least one air-to-liquid heat exchanger from the hot aisle to thecold aisle.
 49. The data center of claim 48, wherein a temperature ofthe hot aisle is between 26 degrees Celsius and 38 degrees Celsius and atemperature of the cold aisle is between 15 degrees Celsius and 25degrees Celsius.
 50. The data center of claim 48, wherein the at leastone fan is at least one first fan; and further comprising an air supplysystem fluidly connected to the room for supplying air from outside theroom to the room, the air supply system including: an air filter; and asecond fan supplying air from outside the room to the room.
 51. A datacenter comprising: a room having a cold aisle and a hot aisle; aplurality of electronic components disposed between the cold aisle andthe hot aisle, air in the room circulating through the plurality ofelectronic components from the cold aisle to the hot aisle; the datacenter cooling system from any one of claims 21 to 47, the at least oneair-to-liquid heat exchanger being disposed between the hot aisle andthe cold aisle; and at least one fan circulating air through the atleast one air-to-liquid heat exchanger from the hot aisle to the coldaisle.
 52. The data center of claim 51, wherein a temperature of the hotaisle is between 26 degrees Celsius and 38 degrees Celsius and atemperature of the cold aisle is between 15 degrees Celsius and 25degrees Celsius.
 53. The data center of claim 51, wherein the at leastone fan is at least one first fan; and further comprising an air supplysystem fluidly connected to the room for supplying air from outside theroom to the room, the air supply system including: an air filter; and asecond fan supplying air from outside the room to the room.